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Forum Index : Electronics : Build a Multi Phase PV Charger and 230Vac Inverter Using Pi Pico
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| Solar Mike Guru  Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
Now that the PI PICO 2 controller is out and readily available here in NZ at reasonable prices, though I would make a start at moving various projects over to it. As my projects have gotten more complex, the old Picaxe CPU's I have used in the past are proving just too slow and lacking in many features of a modern inexpensive 32 bit processor. First project is a 3 phase PV charge controller; the Pico-2 PIO can easily be setup to output 3 PWM phases each running at 125 KHz and driving a buck inverter stage. To that end I want a generic plugin PCB module containing the main CPU and some ancillary components, running off a linear 3.3v psu and ADC reference of 3.0v. Included on the pcb is a voltage rail fail reset chip an MAX809L, this resets low at 4.63v, connected to the incoming 5v power it can cause a interrupt on an input pin and allow the cpu to turn off PIO output pwm signals, shutting down cleanly. Have built this on a small 65x60mm 4-layer pcb with a 44 pin edge connector, so can be plugged in to the main PV host controller. The 4 layers give excellent internal ground and power planes which will help in a noisy inverter environment Schematic:   Have also made a couple of small ancillary helper modules with pin headers. These are on the same 100x100mm pcb and cut off. 1: Trip sensing, this pcb has an over voltage detection comparator to allow shut down of the buck inverters independent of the cpu; as if the output fuse blows or battery gets suddenly disconnected the cpu sensing battery voltage cannot react fast enough to prevent the buck output voltage rising to alarming levels and perhaps destroy components. 2: Low buck current sense, at very low duty cycles its possible for the buck stages act as voltage boosters, feeding battery power backwards causing high voltages on the main capacitors, again blowing things up. To prevent this I switch off the low side synchronous rectifier mosfets at low current levels, thus turning into asynchronous rectification using the mosfets source-drain diode. CPU has no involvement here, buck stage seamlessly switches between the two modes.  The other helper pcb has a I2c ADS1115 mux analog ADC chip and some high input impedance noise filters, again with 8 pin header, main CPU can use this to get accurate voltage measurements, as the PICO-2 still has a slightly compromised ADC input system.  100 x 100 pcb: to cut up at marked edges:   I quite like Micro Python as an object programming language, so will use that for future work using these boards, its also quite fast and allows access to the 2nd CPU, noted with strict limits. Once I have the main CPU board working, will think about the multi-phase buck design, followed by a 230Vac inverter. Edit: just noticed an error on the Max809, will fix it. This is how its meant to be wired, OK on the pcb...  Cheers Mike Edited 2026-06-18 13:25 by Solar Mike |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1285 |
This is very interesting,  I don't think I have seen any standalone chargers like it, I may have some questions later.Will be watching. Cheers Aaron Off The Grid |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
I have made 2 phase chargers in the past, using many RC + schmitt trigger delay stages in series, then tapping off at the correct delay point; but its messy and limited to range of pwm duty values; much easier using the Pico 2 module. Using 3 smaller buck inductors is a lot easier to make also, that and the combined output ripple frequency of 3 x the pwm put a lot less stress on components. Cheers Mike |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
Making a start on this project with the buck inverter modules; each buck output phase will be a 100 x 100mm pcb with bus bar connections to the other 2 phases for PV volts, 0v common and battery output. Will use two TO-247 mosfets on each module mounted under the pcb, so they are pressed against a heat sink - 3mm thick alloy plate - bottom of case or box. To get best gate driver connections its easier to mount the driver components on a separate pcb that solders direct on top of the mosfet pins. Then link these to the PICO controller via 10 pin IDC cables. Here is a test build of the driver module, they are quite small, 4 will fit on a 100x100 pcb. Top:  Bottom:  Concept is quite straight forward, all inputs are high freq filtered then into schmitt trigger NAND gates, the Synchronous signal allows turning off the L0 input during low duty cycles to prevent the buck stage turning into a voltage power booster - Not good, the Disable input via schmitt buffer, turns off the mosfet driver PAI8233c, these are 4 amp fully isolated drivers with resistor set dead time. Small 1w 12-12v psu's provide isolated mosfet bias, note they require min load current (3k Resistor) on output. The main PICO board will turn off the input 12v supply to the 2 PSU's under no charge conditions. I haven't created a schematic for these yet, back of a napkin scribble is all there is currently; and it may not be the final version. More soon.... |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
This is the sort layout of a Buck Module for each output phase, I'm thinking of doing. 20 x 3mm soft alloy bars run under the pcb where the copper pours are tinned, they are bolted to the board by counter-sunk 3mm bolts, this provides great current carrying capacity at little cost; bars are sufficiently long to mount 3 modules. The two power mosfets in each module are placed under the bar area + insulation pad against the heat sink. The driver module sits vertical on the mosfet pins, with their drive ribbon IDC cable running back to the Pico Mother pcb, The bars bolt to one end of the mother board, which has the current sensor and extra bulk electros. Cad Layout PCB 100x100mm:  If say each module handles 30 amps + some ripple current, 3 phases will do 90 amps, this maybe required if running 12 or 24v battery voltages. Three 30 amp buck inductors are much easier to make than 90 amp ones, if 90 amps isn't required then one could just have two phases operating, or leave three and have lots of head room. I don't think I need to worry about having individual current sensing on each module, if the same components are used, currents should be similar, could always have a pwm duty offset on each PICO PIO output to compensate?? Cheers Mike |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
Buck Phase Module 100x100:   Time all three modules + PICO mother board are laid out in a thin alloy box, the physical base size will quite large, if the bottom panel is 2mm thick aluminum, that should be ok for the heat sink, wont require any fins. Work on the Pico mother board next.. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
Main host board done, taken awhile, 2 layer 206w x 170mm pcb. Heavy alloy or copper bars bolt under the pcb against tinned copper pour areas with 5mm spaced via's over the surface. PICO2 cpu module pushes into a 44pin socket, other helper modules solder via header pins, have kept most of the IO logic at 5v using totem pole V translators or HTC logic interfaces, note the I2C uses open drain converters. The PIO generated 3 phase pwm signals are buffered by 74ACT541 so they have enough drive for the ribbon cable outputs to each buck power module. Have allowed for some Bulk input electro's and a few final output ones, testing will tell if I need them all; if not then could have a V2 made smaller. Will do some additional checks and send all the gerbers off in the next day or so. Cad Layout:    Cheers Mike Edited 2026-07-06 15:18 by Solar Mike |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 678 |
Hi Mike, coming from a purely stand alone power standpoint, I am having problems figuring what a multi phase PV charger would be for. To me PV chargers are to charge the batteries for our house. I am wondering if what you are making is your own 3 phase EV charger? I get a bit befuddled by all the coding stuff, having never delved into those dark arts more than making databases and spreadsheets. Pete |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 3321 |
Solar Mike answers that up a few posts Look at it as 3 buck converters synchronized with a 120° phase shift between each. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
Basically we have 3 buck converter modules each driven by 3 pwm inputs 120 degrees apart; so 0, 120, 240 degrees, their outputs are combined into a common DC out, and yes it charges a large Lifepo4 battery bank. The pwm base frequency is 125 kHz, at the combined output the effective frequency ripple is 3 x 125 or 375 kHz. As each pwm power module is only passing 1/3rd of the total output power, its buck inductor can be much smaller than would otherwise be required if a single high powered single phase design was used. Each buck module has 2 mosfets, one for the buck stage and the other for synchronous rectification, with 1/3rd the current there is much less heat dissipated and current sharing is more controllable, the capacitors used can be smaller due to the lower ripple voltages and currents. Note at outputs of less than 2 amps, the synchronous rectification is turned off and each buck reverts to asynchronous to prevent problems with the circuit turning into a reverse boost stage at very low duty cycles. Each buck phase using 2 mosfets should handle 30 odd amps ok, so total output would be around 100 amps continuous, thus the large bus bars joining them together. I wont be using it anywhere near 100 amps, but on say a 24v battery and a modest PV array then that would be a requirement. This is really an experimental learning exercise. Mike Edited 2026-07-06 22:41 by Solar Mike |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 678 |
Thanks Mike, I get it now what you are doing. Good luck with the project, What panel voltages are you planning on feeding into the controller? It looks great, pete |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
I have built a solar carport above the drive down into the garage under the house, mounted 12 by 450 watt bi-facial panels, will arrange in 4 groups of 3 panels as the ones nearest the fence get partial shading in the morning from the house next door. Mppt is 31v so 93v loaded, 106v unloaded, this means I can use 160v capacitors. Pic shows partial construction with 9 up, have since put up the remaining posts and mounted all 12 PV, just have to build a shed next to it for batteries etc. The 3.5m beams across the drive are made from 3 pieces of timber laminated with a steel strip between them, glued with polyurethane, we are in a valley and the winds howls past at times creating a high loading from the panels surface area.  Mike |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 678 |
Looks great Mike, Looking at the photo from this angle the carport looks really low, I was wondering how a car would fit under it. I am guessing that you have no plans to buy a van or a truck and try and get it down the drive. I am thinking the angle of the photo makes it look a lot lower than it is. I understand windy places, we often get 100 kilometre per hour winds in winter where we live, so everything here is over built. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1228 |
The MG EV fits under with plenty of room, a larger SUV + roof rack may have problems, however at some future date, the whole deal can be dismantled; its all held together with bolts and joist hangers with hundreds of stainless screws. The grape vine on the fence didn't produce as many grapes this year, possibly lack of sun, see what its like next year. |
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